package mysql-server-5.7 (not installed) failed to install/upgrade: subprocess new pre-installation script returned error exit status 1

[Rained23]

unable to install mysql or mariadb

ProblemType: Package
DistroRelease: Ubuntu 16.04
Package: mysql-server-5.7 (not installed)
ProcVersionSignature: Ubuntu 4.2.0-35.40-generic 4.2.8-ckt5
Uname: Linux 4.2.0-35-generic x86_64
ApportVersion: 2.19.1-0ubuntu5
Architecture: amd64
Date: Tue Apr 12 13:33:42 2016
DuplicateSignature: package:mysql-server-5.7:(not installed):subprocess new pre-installation script returned error exit status 1
ErrorMessage: subprocess new pre-installation script returned error exit status 1
InstallationDate: Installed on 2016-03-21 (22 days ago)
InstallationMedia: Ubuntu 15.10 "Wily Werewolf" - Release amd64 (20151021)
RelatedPackageVersions:
 dpkg 1.18.4ubuntu1
 apt 1.2.10
SourcePackage: mysql-5.7
Title: package mysql-server-5.7 (not installed) failed to install/upgrade: subprocess new pre-installation script returned error exit status 1
UpgradeStatus: No upgrade log present (probably fresh install)

[Robie Basak (racb)]

From log:

Aborting downgrade from (at least) 10.0 to 5.7.
If are sure you want to downgrade to 5.7, remove the file
/var/lib/mysql/debian-*.flag and try installing again.
dpkg: error processing archive /var/cache/apt/archives/mysql-server-5.7_5.7.11-0ubuntu5_amd64.deb (--unpack):
 subprocess new pre-installation script returned error exit status 1

[Jelle Kalf (j.r.kalf)]

My issue and fix: my /var/lib/mysql is in another location and the /var/lib/mysql is a softlink.

delete /var/lib/mysql-upgrade/DATADIR.link before doing the upgrade and then I had no issue upgrading to 5.7